calculating heat and cooling loads?

[PNWguy]

I am finally about ready to build, and haven't quite decided on how to heat the water for my hydronic (in slab) heating system. Both PV solar and outdoor wood boiler are tempting and have associated pluses and minuses.

I'd like to get a ballpark estimate of what heating loads to expect, as that will help me size the PV system. It's expensive enough that I don't want to overbuild it, and will be unhappy if I throw down many thousands of dollars, and still have a big power bill.

Outdoor wood boilers are not exactly legal here, and if I can avoid cutting firewood, that's a big plus.

The solar installers just ask for 12 months of electric bills, but I haven't built yet. My place is unusual enough that I can't compare it to any other house in my area.

 

[yeldogt]

Sometimes you have to pay to have them done ..... My architect had an HVAC engineering company (one that does commercial building layouts and design) do my current project.

It's important to understand the full building load ....

Do you have NG? Wood is a pain

 

[PNWguy]

Sometimes you have to pay to have them done ..... My architect had an HVAC engineering company (one that does commercial building layouts and design) do my current project.

It's important to understand the full building load ....

Do you have NG? Wood is a pain

I haven't found a company that can do one yet, but my contractor is also looking.

No NG. My options are electric, propane or wood.

I really don't want to rely on propane. It costs an extra dollar a gallon for delivery. A 100 pound tank is the largest (I think) you can legally put into a truck to get filled in town, and that's too small to heat shat much space for very long.

I grew up in a house that burned 6 cords a year, and I'd prefer not to rely on wood. I'm capable of cutting it, and need to cut it regardless (I live on 60 acres, and need to keep the area around the house and the one next door somewhat clear). I also assume with a boiler being more efficient than a wood stove, I'll need less wood than if I was burning it in a wood stove, but I'm trying to heat almost 4,000 sq feet (1,000 of house + 3,000 of shop).

 

[yeldogt]

With full propane use the only way to go is with a 1k tank ... trying to keep up with any kind of portable tank is fools play.

It's all cost .. how much of a given fuel and how much is the fuel. In most parts of the country when NG is not available it's good building practices and the best insulation possible.

with proper insulation 4k of space is reasonable with propane ... mine are spray foamed. Doing it once upfront correctly saves for a lifetime .... more comfort.

 

[ddawg16]

What ever you do....put a lot of consideration into insulation. It is by far your best payback. If you insulate well, you reduce the amount of energy needed to heat or cool the space.

 

[PNWguy]

It's a fully permitted building in the PNW - it will be well insulated. Code requires it, and I'm not a fool.

I want to avoid propane becaue of the 1k tanks. It costs an extra $/gallon to get propane delivered, and I can't legally transport a tank large enough to bother with. I'm not interested in propane as my main heat source.

My two choices are wood and electricity.

 

[kj_mustang]

My 1,000 tank that I purchased gets me cheaper propane than using a leased tank. Paid about $1.50/gallon last July to fill it.

 

[yeldogt]

It's a fully permitted building in the PNW - it will be well insulated. Code requires it, and I'm not a fool.

I want to avoid propane becaue of the 1k tanks. It costs an extra $/gallon to get propane delivered, and I can't legally transport a tank large enough to bother with. I'm not interested in propane as my main heat source.

My two choices are wood and electricity.

Propane does have a delivery charge -- are you saying that where you are located it's particularly expensive ? Where I am it is much more vs NG -- but still half the cost of electric.

What's you electric rate ?

 

[danski0224]

A simple search for "HVAC load calculation" will provide plenty of results.

Terms like "building permit", "professional", "ACCA Manual J", "HERS rater" and so forth can help to narrow results.

There are people nationwide that perform this service, mainly for building permits. You will have to provide a set of specs and drawings.

 

[PNWguy]

Propane does have a delivery charge -- are you saying that where you are located it's particularly expensive ? Where I am it is much more vs NG -- but still half the cost of electric.

What's you electric rate ?

I pay about $0.10/kWh.
LPG is $2.00 - 3.25 a gallon, depending on the season - plus the delivery charge. NG is not available. I will not be using propane for anything other than cooking.

 

[PNWguy]

A simple search for "HVAC load calculation" will provide plenty of results.

Terms like "building permit", "professional", "ACCA Manual J", "HERS rater" and so forth can help to narrow results.

There are people nationwide that perform this service, mainly for building permits. You will have to provide a set of specs and drawings.

That search has provided many results, and most of them are terrible programs without enough control over the variables (I don't heat my shop and garage to the same temp as my house, for example).

I was hoping that somebody here had used one and could offer a recommendation.

 

[danski0224]

I did a search for this "hvac load calculation for permit" and came up with several viable results that aren't computer programs.

HVAC-Calc is available as a single use license for a low cost for DIY.

 

[yeldogt]

I pay about $0.10/kWh.
LPG is $2.00 - 3.25 a gallon, depending on the season - plus the delivery charge. NG is not available. I will not be using propane for anything other than cooking.

In my area I factor a high of around $2.50g for propane in recent years (it's been less). With .10kw electric you are at my propane cost. My electric is 2x your electric cost -- so using electric (unless a heat pump) is expensive.

Depending on how cold you get -- heat pumps may be a viable way to go with an electric boiler just to warm the floors. Air to water heat pumps are expensive and not widely available.

 

[PNWguy]

Electrical will cost more, but for $12-$15k I can cover my roof with solar panels. As far as I know, there's no propane collector I can add to my house.

If I know the heat & cooling loads, I can determine if the proposal from the solar company is worth perusing. The idea of spending $15,000 today to never have a power bill again is worth it to me. In addition, another $8,000 would purchase a battery that would run my house for a day, and magically refills itself - for no cost.

 

[yeldogt]

.10 electric is equal to $2.50 propane ... that's why I mentioned it. Since my electric is .20 KW .. Propane is a lot cheaper vs electric. Except ... Heat pumps will get me 3x the efficiency over straight resistance. So under Ideal conditions ... I'm running a bit under .7KW with the heat pumps running.

But, have to maintain temps as heat pumps don't have quick recovery and I also have radiant heat (because I like it) -- need boiler. The house is 4k+ and my studio is around 1800sf. The house needs about 52k BTU and the studio can actually run at under 20k BTU (mostly SIP) .. but it has 32k BTU propane. The house is spray foamed. The house has both a boiler for the radiant/DHW and ducted/ mini-split heap pumps for AC ... I run the ducted HP when turning on the radiant would take too long and to also smooth out the temps -- same with the mini-splits. Since I had to install the ducted system for AC -- the cost to install a furnace was only about 2.5k more. So I can heat the house with propane forced air or radiant or HP electric.

I don't use it full time now -- but will in the future. It's a bit rural .. and I decided to get a generator. So having the propane was important as trying to run the HP's off the generators is not going to work. Generator is propane.

I looked into solar -- and Geothermal. The numbers don't work. The payback was 15 and 20 years respectively (with rebates) just the house -- and the solar would not do the whole house heating and 5T AC . So I still needed the backups -- and the studio.

I'm not sure how unusual. Typically you can punch in base numbers -- type of insulation. Glass area and come up with a number. Where it's important to get exact is when you are doing a room by room with very different loads. I'm doing an odd building where some of the rooms will have exposed stone and other rooms have few windows and 30' ceilings -- it's zoned for comfort ..so we had to model it. But doing the full house load was not hard as we plugged in the walls and roof ... floors and glass ares .

 

[PNWguy]

I'd rather use hydronic than a heat pump, but that's why I need to figure out the loads.

One of the biggest problems I have with the software is that it tends to calculate how many BTUs I'll need on the hottest and coldest days so I can size my HVAC system. Those numbers don't really do me any good, as I'm trying to get an estimate how many kWh per year I'll use (ballpark, on average).

My space is a 1200 sq ft shop with 12' ceilings, a 400 sq ft woodshop with 10' ceilings, a 625 sq ft garage with 10' ceilings and a 990 sq foot house with 10' ceilins (and lots of glass) - as well as 800 sq ft on the second story for a bedroom & office. 3,200 sq feet of slab + 800 upstairs.

I'll have 4 downstairs heating zones, and one upstairs. All of it is slab on grade (except upstairs of course).

The living space walls will most likely by 2x8 with blown in bat insulation, and the rest will be 2x6. Metal roof (lots of heat reflection). It's somewhat complicated - and the software I've found is trying to answer a different question than I'm asking.

 

[MattT]

I'd rather use hydronic than a heat pump, but that's why I need to figure out the loads.

Looks like you'll need some air conditioning so may as well upgrade to a heat pump to get some heat at ~1/3 the cost. Aside from the cost I also think a heat pump will regulate temperature better in spring and fall with the extreme swings it looks like y'all get.

One of the biggest problems I have with the software is that it tends to calculate how many BTUs I'll need on the hottest and coldest days so I can size my HVAC system. Those numbers don't really do me any good, as I'm trying to get an estimate how many kWh per year I'll use (ballpark, on average).

You can use heating and cooling degree days to estimate annual loads. Just bear in mind it's just an estimate calculated from the Man J estimate so it could be off by quite a bit.

https://www.degreedays.net/

http://www.greenbuildingtalk.com/Forums/tabid/53/aff/21/aft/82939/afv/topic/Default.aspx

 

[yeldogt]

PNWguy .. as MattT indicated you have to go further into the design detail to get the degree days. room by room heat/cooling loads and duct design -- hydronic loop design.

You have to know the outside parameters. The vast majority of houses are a big guess -- 80k or 100k furnace ductwork based on common sizes and what will fit.

Trying to figure out if solar will work or is cost effective comes after you know what the building is going to use. You can't base your heater on what the solar will provide ?

I also looked into an air to water heat pump to run the hydronic .... the cost of the unit and controls made it a non starter. Again -- with proper insulation the savings even at my higher costs for electric are not there.

The metal roof is not going to make any real difference -- use what you have and punch teh numbers into the programs ... same with 10' ceilings on the heat side w/ radiant ... it's not going to make any real difference. It's when you have spray foam that the programs can have problems -- need a qualified person.. Spray eliminates air leaking. I'm assuming "blown in batt" is some form of loose fiberglass? Cell? Put in the sf of windows.

The key with what you are doing is to understand the slab -- have enough control of it and be able to zone it properly when it's not near design temps ... otherwise it will overheat the space.

 

[Showkey]

One way to look into the future.......look at other states. The push to electric vehicles will raise electric rates by at least 50%-100% in many locations.
If your really serious about conservation and controlling future cost design and rebuild towards the net zero concept or green design standards. Of course it’s going to cost double to triple in today’s build cost but it your staying put, you may see the pay off.

When I was buying my current home, propane was $4.00-$4.50 gallon.

If your going with electric, tighten the home to the highest standards. Then shop the heat pump.

 

[PNWguy]

Looks like you'll need some air conditioning so may as well upgrade to a heat pump to get some heat at ~1/3 the cost. Aside from the cost I also think a heat pump will regulate temperature better in spring and fall with the extreme swings it looks like y'all get.



You can use heating and cooling degree days to estimate annual loads. Just bear in mind it's just an estimate calculated from the Man J estimate so it could be off by quite a bit.

https://www.degreedays.net/

http://www.greenbuildingtalk.com/Forums/tabid/53/aff/21/aft/82939/afv/topic/Default.aspx

I'll put a mini split in the upstairs bedroom, but not in other places. I'm out in the forest, with no concrete, asphalt and buildings to hold the heat in - it's normally 10 degrees warmer "in town" in the daytime, and much warmer at night. We leave the windows open at night, and the house is cold in the mornings. Close the windows at 10:00 AM, and it stays cool all day. Because forest fire season has gone from 2 months to 6 months in the last 10 years, I'll put in a mini split in the bedroom, in case I want to keep the smoke out and leave the windows closed.

For the shop, I don't really care about temp swings. I think a warm slab will help equalize it. Even the shop will be well insulated.

My new place is probably the last place I'll live, and I'm willing to put the cash up front so I can live comfortably on retirement as long as I'm there.

 

[PNWguy]

One way to look into the future.......look at other states. The push to electric vehicles will raise electric rates by at least 50%-100% in many locations.
If your really serious about conservation and controlling future cost design and rebuild towards the net zero concept or green design standards. Of course it’s going to cost double to triple in today’s build cost but it your staying put, you may see the pay off.

When I was buying my current home, propane was $4.00-$4.50 gallon.

If your going with electric, tighten the home to the highest standards. Then shop the heat pump.

It won't cost double or triple to build "green" in Oregon; our code is already pretty strong that way. About the only thing I'll be doing that isn't required is insulating the shop. It looks like I'll be required to have 2x8 walls (to get a high enough R value) in the house. As I said, Oregon is pretty serious about codes already.

Since we have net metering and 16 hours of sun all summer, I can build massive credit on my electric bill all summer, and draw from it during the winter.

 

[Showkey]

We had net metering here..........it did not last. Changed the landscape, where it only made sense to produce what you need.

 

[yeldogt]

Net metering w/ carryover and the rebates was still 15 years when it was all available at my place in NJ. It does work better w/ modest size house.

Frankly -- how we subsidize the solar industry is not cost effective or fair. Net metering provides free delivery both way to the solar owner ..while increasing cost to the non owner. The grid is free to the net operator.

Smaller more standard systems able to provide partial and optimized to provide excess when a house needs it ... not the max it can provide is what's needed to smooth out the grid.

 

[danski0224]

You will need to get the heating and cooling degree days, and do some math:

http://solar365.com/green-homes/heating-ac/heating-degree-days-heat-load-analysis

This will get you an average btu per degree day.

Then you have more math to do.... probably btu to kw, which will vary based upon what you are using to heat/cool.

 

[kalyanram]

Great innovation

 

[yeldogt]

You will need to get the heating and cooling degree days, and do some math:

http://solar365.com/green-homes/heating-ac/heating-degree-days-heat-load-analysis

This will get you an average btu per degree day.

Then you have more math to do.... probably btu to kw, which will vary based upon what you are using to heat/cool.

This is how oil and propane companies factor auto deliveries to keep you tanks filled. With a couple years of usage the number are extremely accurate ... that's why the solar companies want the utility bills.

Unfortunately, with no use available on a new build .. there is only a guess available